The present invention relates generally to commutation of large amounts of electrical current and particularly to commutating current to superheat a moving rod or bar of element material employed in alloying a molten metal media, such as molten aluminum, though the invention is not limited thereto.
In U.S. Pat. No. 4,688,771 to Eckert et al, an alloying material in the form of a wire 10 is shown directed to a molten media 12. (This patent is one of several U.S. patents to Eckert et al on alloying. To list all of the patents which here would be unduly repetitive.) Between the end of the wire adjacent the molten media and the media itself is a difference of a potential created by a power supply 36. This difference in potential causes a spark or arc to be formed between the wire and the molten media for the purpose of adding the alloying element or elements of the wire to the media in a manner that greatly enhances the alloying process. Such a process requires a substantial amount of electrical current to superheat the wire, and this current must be "commutated" to the wire from the electrical supply with minimal resistance to the flow of the current.
Heretofore, such current was usually commutated through stationary contact tubes, such as shown in the Eckert et al patent or through stationary "shoes", such as shown at 44 in U.S. Pat. No. 3,836,360 to Bray. Bray suggests using feed rollers to apply current to a master alloy feed wire in place of contact member 44 but prefers the non-rotating member for the reasons stated in the patent.
A common application of current transferring shoes is in the welding industry where a wire or rod of filler material, usually on the order of one-eighth inch diameter, is directed to a welding area. The rod functions as one electrode for developing a welding arc between it and the material to be welded. Such applications of current are generally (1) intermittent in nature, (2) require high quality electrode (wire) material, and require frequent changing of the stationary tubes or shoes because of the wear caused by friction occurring between the welding wire and shoes, and because the shoes collect wire material as the wire passes therethrough. Relative speed between a welding wire or rod and contact shoes is generally low, less than 2,000 inches per minute, with relatively low current requirements, using less than 1,000 amperes, and with current densities on the order of 200,000 amps per square inch.
A system being tested by Applicants for on-line alloying purposes, using one-quarter inch diameter lead bismuth rod requires current of 500 to 600 amps and a maximum speed of 960 inches per minute for periods of about one hour. In such a system, sliding (stationary) shoe commutators are adequate. However, when conditions are altered to use a one quarter inch diameter magnesium rod with current demands of 3,000 to 7,000 amps at speeds of 2200 inches per minute and current densities in excess of one million amps per square inch for extended periods of time, sliding shoes are not adequate and have led to the development and invention described below.
A sliding shoe requires high quality rod material in order to successively commutate an adequate amount of electrical current to the rod. A high quality rod is one in which there are minimum or no surface defects, such as checks, nicks or slices, or other types of scratches or flaws in the rod surface. Worn drawing dies, for example, leave "draw lines" that extend lengthwise of a rod.
Another element of quality is the cleanliness of the rod. Insulating substances, such as lubricants and oxides collect on the surfaces of the shoes and rod thereby interfering with current flow. In other words, both the surface of the shoe and the surface of the rod should be as smooth and clean as possible in order to adequately transfer electrical current.